Hydroformylation is a well known and commercially practiced process in which an olefinically unsaturated organic compound is contacted and reacted with a mixture of carbon monoxide and hydrogen, and thereby converted to a corresponding aldehyde or alcohol. In general, hydroformylation may be illustrated by the following equation: ##STR1## Frequently, hydroformylation is accompanied by some degree of isomerization of the carbon-carbon double bond position, resulting in several other aldehyde and alcohol structures in addition to those illustrated. In the above equation, each R represents, independently, an organic radical, or other substituent, e.g., a hydrogen or halogen atom, a hydroxyl group, a carbonyl group, a carboxyl group, etc, which does not interfere with the intended reaction at the double bond.
At present, rhodium catalyzed hydroformylation reactions are most commonly applied for the conversion of lower carbon number (e.g., C.sub.3 to C.sub.5) olefins to aldehydes, but are known to be applicable to the conversion of a wide range of other olefinically unsaturated reactants.
This invention most particularly relates to hydroformylation in the presence of a heterogeneous catalyst, comprising a rhodium complex supported on a solid surface. In conventional practice, hydroformylation reactions have, almost exclusively, utilized homogeneous rather than heterogeneous catalysts. The use of homogeneous catalysts for hydroformylation provides relatively high activity and selectivity at mild reaction conditions, but suffers from the difficulties inherent in the recovery of homogeneous catalysts from the reaction products. Because of the value of the metal, extremely effective catalyst recovery has been a necessity when dealing with homogeneous catalysts containing rhodium compounds and/or complexes. Moreover, the requirements for product purity have also been an important factor dictating effective catalyst removal from specialty chemical products of rhodium catalyzed hydroformylation. Procedures available in the art for recovery of homogeneous catalysts often prove to be difficult and/or expensive. In many cases, the requirements for catalyst recovery limit the commercial opportunities for the application of rhodium catalysts.
Although the difficulties inherent in the use of homogeneous hydroformylation catalysts have long provided incentive for the development of heterogeneous catalysts, attempts in the art to make use of heterogeneous rhodium catalysts have been largely unsuccessful, either because of leaching of rhodium from solid supports during the process or because of unacceptably low catalyst activity.
In other aspects, the present invention relates to a hydroformylation process carried out in the presence of a catalyst comprising a rhodium complex in a polar solvent (e.g., water) solution, which is essentially immiscible with the olefinically unsaturated organic reactant phase. U.S. Pat. No. 4,248,802 describes a catalytic system for hydroformylation which comprises a rhodium containing aqueous solution of certain sulfonated phosphine compounds. Rhodium is present either as metallic rhodium deposited on a support material, or in the form of water soluble compound or complex. The patent fails to teach or suggest a catalyst wherein a rhodium complex solution is supported on a solid. Nor do the teachings of this patent specify an aqueous rhodium complex solution which is essentially immiscible with the organic reactant phase. Instead, it is said to be of advantage in the process of U.S. Pat. No. 4,248,802 to add solvents (e.g., lower alcohols, ketones, nitriles and ethers) which increase the solubility of olefinic reactants in the aqueous catalyst solution.
Borowski et al (Nouveau, J. Chemie 2, 137 (1978)) also describe the preparation and use as hydroformylation catalysts of rhodium complexes dissolved in water. For hydroformylation, aqueous complex solutions are dispersed by mixing into an immiscible organic reactant phase. The publication does not contemplate immobilizing such complexes on solid support surfaces.